Project Summary The proposed study will investigate the role of cerebrovascular dysfunction during the earliest stages of neurocognitive decline, prior to any obvious changes in cognition. Specifically, we will study whether cognitively normal older adults at risk for Alzheimer's disease show increased cerebrovascular resistance. We will also study how increased cerebrovascular resistance relates to brain dysfunction using functional brain scans. Finally, we will investigate whether higher cerebrovascular resistance in cognitively normal older adults predicts development of subtle cognitive decline over a two year follow-up interval.